Tool compressed insert for closure independent locking of a pivotal bone anchor assembly
A polyaxial bone screw assembly includes a threaded shank body having an integral upper portion receivable in an integral receiver, the receiver having an upper channel for receiving a longitudinal connecting member and a lower cavity cooperating with a lower opening. The receiver can have crimp tabs, but is devoid of spring tabs and collet-like flexible structures. A down-loadable compression insert (some with lock and release feature), a down-loadable friction fit split retaining ring and an up-loadable shank upper portion cooperate to provide for pop- or snap-on assembly of the shank with the receiver either prior to or after implantation of the shank into a vertebra. The shank and receiver once assembled cannot be disassembled. The receiver and insert include aligned tool receiving apertures for lock and release of the polyaxial mechanism.
1. A pivotal bone anchor assembly for securing an elongate rod to a bone with a closure via closure independent locking with an insert compressing tool, the pivotal bone anchor assembly comprising:
a receiver having a base defining a cavity communicating with a bottom opening, and a pair of upright arms extending upwardly from the base to define an open channel for receiving the elongate rod, the open channel communicating with the cavity to define a central bore, the pair of upright arms including:
opposed inward-facing surfaces having a discontinuous helically wound closure-mating structure formed therein; and
outward-facing surfaces having receiver tool engagement structures formed therein for releasable overlapping engagement with the insert compressing tool;
a bone anchor having a capture portion pivotally disposed within the receiver cavity and an anchor portion extending distally from the capture portion and through the receiver bottom opening for fixation to the bone; and
a compression insert at least partially disposed within the receiver center bore and having an upper surface configured for engagement with the elongate rod, the insert having a central opening and upward-facing surfaces on tool engagement structures positioned radially outward from the central opening,
wherein the the receiver tool engagement structures and the insert upward-facing tool engagement structures are configured for simultaneous non-threadable engagement and downward compressing engagement, respectively, by the insert compressing tool, thereby applying a downward force to independently lock a position of the bone anchor with respect to the receiver prior to securing the elongate rod within the receiver open channel via the closure, and
wherein the closure is positionable within the channel while the position of the bone anchor with respect to the receiver is so independently locked by the insert compressing tool.
2. The pivotal bone anchor assembly of claim 1 , wherein the insert compressing tool is operable to maintain a downward bias of the compression insert within the receiver during installation of the elongate rod and the closure into the receiver open channel.
3. The pivotal bone anchor assembly of claim 1 , wherein the insert tool engagement structure upward-facing surfaces are not covered by the elongate rod or by the closure.
4. The pivotal bone anchor assembly of claim 1 , wherein the insert tool engagement structure upward-facing surfaces are positioned diametrically opposite of each other.
5. The pivotal bone anchor assembly of claim 4 , wherein the insert compressing tool further comprises downward-facing surfaces complementary with the insert upward-facing surfaces on the compression insert.
6. The pivotal bone anchor assembly of claim 5 , wherein the insert upward-facing surfaces and the insert compressing tool downward -facing surfaces are substantially planar.
7. The pivotal bone anchor assembly of claim 1 , further comprising side apertures extending through the receiver upright arms below the discontinuous helically wound closure-mating structure from the opposed inward-facing surfaces to the outward-facing surfaces.
8. The pivotal bone anchor assembly of claim 7 , wherein the insert tool engagement structures are located proximate to the receiver side apertures for direct access by the insert compressing tool.
9. The pivotal bone anchor assembly of claim 7 , wherein each of the side apertures further includes a tool alignment surface for guiding the insert compressing tool to the insert tool engagement structures.
10. The pivotal bone anchor assembly of claim 9 , wherein tool alignment surface is sloped.
11. The pivotal bone anchor assembly of claim 1 , wherein the compression insert is downloadable into the receiver channel.
12. The pivotal bone anchor assembly of claim 1 , wherein the compression insert further includes oppositely-directed opposed radial extensions in the direction of the receiver channel to extend an insert channel supporting surface for the elongate rod.
13. The pivotal bone anchor assembly of claim 12 , wherein the opposed radial extensions have lateral surfaces configured to engage an inner sidewall surface of the receiver upright arms so as to block rotation between the compression insert and the receiver.
14. The pivotal bone anchor assembly of claim 1 , wherein the insert compressing tool further comprises an actuation member for moving a distal end portion into engagement with the insert tool engagement structures, the actuation member being selected from the group consisting of a pistol grip tool, a hinged tool, and a rotatably threaded device.
15. The pivotal bone anchor assembly of claim 1 , further comprising an interference structure formed into the receiver central bore below the discontinuous helically wound closure mating structure and extending inward toward a longitudinal center axis of the receiver.
16. The pivotal bone anchor assembly of claim 15 , wherein the compression insert includes an exterior surface configured to engage the receiver interference structure in a forced interference engagement so as to prevent the compression insert from moving back up within the receiver central bore.
17. The pivotal bone anchor assembly of claim 1 , wherein the bone anchor further comprises a cannulated shank with a central opening extending along an entire length thereof.
18. The pivotal bone anchor assembly of claim 1 , further comprising a retainer positionable within the receiver cavity prior to the bone anchor capture portion and operable to capture the bone anchor capture portion upon the uploading of the bone anchor capture portion through the bottom opening.
19. The pivotal bone anchor assembly of claim 18 , wherein the retainer is non-pivotal with respect to the receiver after the capture of the bone anchor capture portion.
20. The pivotal bone anchor assembly of claim 1 , further comprising the closure, and wherein the closure includes a helically wound guide and advancement structure formed into an outer sidewall surface and engageable with the discontinuous helically wound closure-mating structure formed into the opposed inward-facing surfaces of the receiver upright arms to capture the elongate rod within the receiver open channel.